The present study was performed on farm animals to test the effectiveness of progesterone-releasing intravaginal device (Cue-Mate® 1.56 g) and injection of prostaglandin F2α (PGF2α) for synchronization estrus in Hanwoo cattle. The cattle were at random stage of the estrus cycle. The cows were artificially inseminated at day 7 after Cue-Mate withdrawal, using commercial semen from Korean native bulls. There was a season effect on the estrus synchronization rate. It was higher in spring (94.3%) followed by winter (93.3%), autumn (90.4%) and summer (67.2%). In summary, The results of this study revealed that season has influences on estrus behavior of cattle with no significant effect on pregnancy rate. In summary, we suggest summer reproductive management to alleviate the effects of heat stress. It should be based on intensive cooling combined with hormonal treatment. Given that different subgroups of cows benefit differently from the treatments, selective hormonal administration should be considered.

• Sang-Rae Cho(Hanwoo Experiment Station, National Institute of Animal Science, RDA) Corresponding author
• Kuldeep Kumar(Hanwoo Experiment Station, National Institute of Animal Science, RDA)
• Seong-Heum Yeon(Hanwoo Experiment Station, National Institute of Animal Science, RDA)
• Sung-Hwan Lee(Hanwoo Experiment Station, National Institute of Animal Science, RDA)
• Ui-Hyung Kim(Hanwoo Experiment Station, National Institute of Animal Science, RDA)
• Ki-Yong Chung(Hanwoo Experiment Station, National Institute of Animal Science, RDA)
• Hyeon-Shup Kim(Hanwoo Experiment Station, National Institute of Animal Science, RDA)
• Myeung Sik Lee(Hanwoo Experiment Station, National Institute of Animal Science, RDA)
• Chang-Seok Park(Hanwoo Experiment Station, National Institute of Animal Science, RDA)
• Byoung-Chul Yang(Hanwoo Experiment Station, National Institute of Animal Science, RDA)